The invention relates to devices for displacing and holding a cluster of control elements movable vertically in the core of a nuclear reactor, such a cluster being part of a set of two coaxially movable clusters fulfilling different functions.
With such sets, driving, power, control regulation, compensation of fuel exhaustion and shut down of a nuclear reactor can be better assured. Particularly, sets in which one of the clusters is formed of so called "black" elements having very high neutron absorption and the other clusters is formed of "grey" elements, have been proposed. The cluster of "black" elements is inserted in the core of the reactor by lowering it into it lowest position thus for shutting down the reaction and maintining it stopped. The displacement device may be partially shared by both clusters (French Pat. No. 2 106 373). It has also been proposed to have a separate device for each cluster (French Pat. No. 2537 764) one cluster including absorbent element and the other cluster elements containing fertile material. But none of the prior arrangements allows full freedom of displacement of one of the clusters, when the other cluster is in one of its endmost positions, except if complex mechanisms are installed.